2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[PatSyntax]{Abstract Haskell syntax---patterns}
8 Pat(..), InPat, OutPat, LPat,
10 HsConDetails(..), hsConArgs,
12 mkPrefixConPat, mkCharLitPat, mkNilPat,
15 patsAreAllCons, isConPat, isSigPat,
16 patsAreAllLits, isLitPat, isIrrefutableHsPat
19 #include "HsVersions.h"
22 import {-# SOURCE #-} HsExpr ( SyntaxExpr )
25 import HsBinds ( DictBinds, emptyLHsBinds, pprLHsBinds )
26 import HsLit ( HsLit(HsCharPrim), HsOverLit )
27 import HsTypes ( LHsType, PostTcType )
28 import BasicTypes ( Boxity, tupleParens )
30 import PprCore ( {- instance OutputableBndr TyVar -} )
31 import TysWiredIn ( nilDataCon, charDataCon, charTy )
33 import DataCon ( DataCon, dataConTyCon )
34 import TyCon ( isProductTyCon )
37 import SrcLoc ( Located(..), unLoc, noLoc )
42 type InPat id = LPat id -- No 'Out' constructors
43 type OutPat id = LPat id -- No 'In' constructors
45 type LPat id = Located (Pat id)
48 = ------------ Simple patterns ---------------
49 WildPat PostTcType -- Wild card
50 | VarPat id -- Variable
51 | VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
52 -- bindings give its overloaded instances
53 | LazyPat (LPat id) -- Lazy pattern
54 | AsPat (Located id) (LPat id) -- As pattern
55 | ParPat (LPat id) -- Parenthesised pattern
57 ------------ Lists, tuples, arrays ---------------
58 | ListPat [LPat id] -- Syntactic list
59 PostTcType -- The type of the elements
61 | TuplePat [LPat id] -- Tuple
62 Boxity -- UnitPat is TuplePat []
64 | PArrPat [LPat id] -- Syntactic parallel array
65 PostTcType -- The type of the elements
67 ------------ Constructor patterns ---------------
68 | ConPatIn (Located id)
69 (HsConDetails id (LPat id))
71 | ConPatOut (Located DataCon)
72 [TyVar] -- Existentially bound type variables
73 [id] -- Ditto dictionaries
74 (DictBinds id) -- Bindings involving those dictionaries
75 (HsConDetails id (LPat id))
76 Type -- The type of the pattern
78 ------------ Literal and n+k patterns ---------------
79 | LitPat HsLit -- Used for *non-overloaded* literal patterns:
80 -- Int#, Char#, Int, Char, String, etc.
82 | NPat (HsOverLit id) -- ALWAYS positive
83 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
84 -- patterns, Nothing otherwise
85 (SyntaxExpr id) -- Equality checker, of type t->t->Bool
86 PostTcType -- Type of the pattern
88 | NPlusKPat (Located id) -- n+k pattern
89 (HsOverLit id) -- It'll always be an HsIntegral
90 (SyntaxExpr id) -- (>=) function, of type t->t->Bool
91 (SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
93 ------------ Generics ---------------
94 | TypePat (LHsType id) -- Type pattern for generic definitions
95 -- e.g f{| a+b |} = ...
96 -- These show up only in class declarations,
97 -- and should be a top-level pattern
99 ------------ Pattern type signatures ---------------
100 | SigPatIn (LPat id) -- Pattern with a type signature
103 | SigPatOut (LPat id) -- Pattern with a type signature
106 ------------ Dictionary patterns (translation only) ---------------
107 | DictPat -- Used when destructing Dictionaries with an explicit case
108 [id] -- superclass dicts
112 HsConDetails is use both for patterns and for data type declarations
115 data HsConDetails id arg
116 = PrefixCon [arg] -- C p1 p2 p3
117 | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
118 | InfixCon arg arg -- p1 `C` p2
120 hsConArgs :: HsConDetails id arg -> [arg]
121 hsConArgs (PrefixCon ps) = ps
122 hsConArgs (RecCon fs) = map snd fs
123 hsConArgs (InfixCon p1 p2) = [p1,p2]
127 %************************************************************************
131 %************************************************************************
134 instance (OutputableBndr name) => Outputable (Pat name) where
137 pprPatBndr :: OutputableBndr name => name -> SDoc
138 pprPatBndr var -- Print with type info if -dppr-debug is on
139 = getPprStyle $ \ sty ->
140 if debugStyle sty then
141 parens (pprBndr LambdaBind var) -- Could pass the site to pprPat
142 -- but is it worth it?
146 pprPat :: (OutputableBndr name) => Pat name -> SDoc
148 pprPat (VarPat var) = pprPatBndr var
149 pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
150 pprPat (WildPat _) = char '_'
151 pprPat (LazyPat pat) = char '~' <> ppr pat
152 pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
153 pprPat (ParPat pat) = parens (ppr pat)
155 pprPat (ListPat pats _) = brackets (interpp'SP pats)
156 pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
157 pprPat (TuplePat pats bx) = tupleParens bx (interpp'SP pats)
159 pprPat (ConPatIn con details) = pprUserCon con details
160 pprPat (ConPatOut con tvs dicts binds details _)
161 = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a
162 if debugStyle sty then -- typechecked Pat in an error message,
163 -- and we want to make sure it prints nicely
164 ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
165 pprLHsBinds binds, pprConArgs details]
166 else pprUserCon con details
168 pprPat (LitPat s) = ppr s
169 pprPat (NPat l Nothing _ _) = ppr l
170 pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
171 pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
172 pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
173 pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
174 pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
175 pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
176 brackets (interpp'SP ds),
177 brackets (interpp'SP ms)])
179 pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
180 pprUserCon c details = ppr c <+> pprConArgs details
182 pprConArgs (PrefixCon pats) = interppSP pats
183 pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
184 pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
186 pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
189 -- add parallel array brackets around a document
191 pabrackets :: SDoc -> SDoc
192 pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
196 %************************************************************************
200 %************************************************************************
203 mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id
204 -- Make a vanilla Prefix constructor pattern
205 mkPrefixConPat dc pats ty = noLoc $ ConPatOut (noLoc dc) [] [] emptyLHsBinds (PrefixCon pats) ty
207 mkNilPat :: Type -> OutPat id
208 mkNilPat ty = mkPrefixConPat nilDataCon [] ty
210 mkCharLitPat :: Char -> OutPat id
211 mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
215 %************************************************************************
217 %* Predicates for checking things about pattern-lists in EquationInfo *
219 %************************************************************************
221 \subsection[Pat-list-predicates]{Look for interesting things in patterns}
223 Unlike in the Wadler chapter, where patterns are either ``variables''
224 or ``constructors,'' here we distinguish between:
227 Patterns that cannot fail to match: variables, wildcards, and lazy
230 These are the irrefutable patterns; the two other categories
231 are refutable patterns.
234 A non-literal constructor pattern (see next category).
236 \item[literal patterns:]
237 At least the numeric ones may be overloaded.
240 A pattern is in {\em exactly one} of the above three categories; `as'
241 patterns are treated specially, of course.
243 The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
245 isWildPat (WildPat _) = True
246 isWildPat other = False
248 patsAreAllCons :: [Pat id] -> Bool
249 patsAreAllCons pat_list = all isConPat pat_list
251 isConPat (AsPat _ pat) = isConPat (unLoc pat)
252 isConPat (ConPatIn _ _) = True
253 isConPat (ConPatOut _ _ _ _ _ _) = True
254 isConPat (ListPat _ _) = True
255 isConPat (PArrPat _ _) = True
256 isConPat (TuplePat _ _) = True
257 isConPat (DictPat ds ms) = (length ds + length ms) > 1
258 isConPat other = False
260 isSigPat (SigPatIn _ _) = True
261 isSigPat (SigPatOut _ _) = True
262 isSigPat other = False
264 patsAreAllLits :: [Pat id] -> Bool
265 patsAreAllLits pat_list = all isLitPat pat_list
267 isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
268 isLitPat (LitPat _) = True
269 isLitPat (NPat _ _ _ _) = True
270 isLitPat (NPlusKPat _ _ _ _) = True
271 isLitPat other = False
273 isIrrefutableHsPat :: LPat id -> Bool
274 -- This function returns False if it's in doubt; specifically
275 -- on a ConPatIn it doesn't know the size of the constructor family
276 -- But if it returns True, the pattern is definitely irrefutable
277 isIrrefutableHsPat pat
280 go (L _ pat) = go1 pat
282 go1 (WildPat _) = True
283 go1 (VarPat _) = True
284 go1 (VarPatOut _ _) = True
285 go1 (LazyPat pat) = True
286 go1 (ParPat pat) = go pat
287 go1 (AsPat _ pat) = go pat
288 go1 (SigPatIn pat _) = go pat
289 go1 (SigPatOut pat _) = go pat
290 go1 (TuplePat pats _) = all go pats
291 go1 (ListPat pats _) = False
292 go1 (PArrPat pats _) = False -- ?
294 go1 (ConPatIn _ _) = False -- Conservative
295 go1 (ConPatOut (L _ con) _ _ _ details _)
296 = isProductTyCon (dataConTyCon con)
297 && all go (hsConArgs details)
299 go1 (LitPat _) = False
300 go1 (NPat _ _ _ _) = False
301 go1 (NPlusKPat _ _ _ _) = False
303 go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
304 go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"